1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine tool, and more particularly, to a numerical controller with a function to correct a movement path of a machining program.
2. Description of the Related Art
A machining program for die and mold machining created by computer-aided manufacturing (CAM) or the like contains pick-feed blocks that connect adjacent movement paths. Pick-feed blocks are generally located in a non-cutting area in the case that a tool is reciprocated for cutting operation, as shown in FIG. 18. In the case of cutting along contour lines, as shown in FIG. 19, in contrast, many of pick-feed blocks are located in a cutting area. In either case, the pick-feed blocks and their adjacent blocks should preferably be smoothly connected. This is because unnecessary speed reduction may sometimes be caused by corner deceleration at a pick-feed section, acceleration clamp, or the like in the case of such a machining program that the pick-feed blocks and their adjacent blocks are not smoothly connected. If the machining program is such that pick-feed blocks are in a non-cutting area, the machining efficiency is reduced when speed reduction occurs at the pick-feed section. If the machining program is such that the pick-feed blocks are in a cutting area, on the other hand, the machined surface of a workpiece is adversely affected by cutter marks or the like when speed reduction occurs at the pick-feed section.
A technique for smoothly connecting pick-feed blocks and their adjacent blocks is disclosed in Japanese Patent Application Laid-Open No. 2007-200037. According to this technique, as shown in FIG. 20, a pick-feed section is extracted from a machining program, and paths at the pick-feed section and its adjacent air-cut sections are replaced with a high-order NURBS curve whose curvature is continuous at any point on the curve. According to the machining program with pick-feed blocks in a non-cutting area, based on this technique, speed reduction is suppressed at the pick-feed section, so that the machining efficiency can be improved.
However, the technique disclosed in Japanese Patent Application Laid-Open No. 2007-200037 is not assumed to be applied to such a machining program that pick-feed blocks are located in a cutting area. Further, this technique has a problem that it is not possible to apply to a machining program in which the pick-feed section comprises a plurality of blocks.
Thus, according to the machining program in which pick-feed blocks are located in a cutting area, the influence of speed reduction at the pick-feed section is minimized by re-creating the machining program, based on CAM that can create a movement path without a pick-feed block in the process of machining program creation, or by increasing the post-interpolation acceleration/deceleration time constant or reducing the cutting speed. However, the mold shape precision is reduced according to the method in which the post-interpolation acceleration/deceleration time constant is increased. According to the method in which the cutting speed is reduced, on the other hand, machining time is unreasonably long.